gaybro8777/autofdo

AutoFDO

Introduction

The repository contains a tool to convert perf.data profile to AutoFDO profile that can be used by GCC and LLVM.

Each compiler is supported by a different tool. For GCC, use create_gcov. For LLVM, use create_llvm_prof. LLVM version 5 or higher is required. The two tools have compatible command line flags. However, the outputs are incompatible. You cannot use the profile generated for GCC in LLVM and vice-versa.

Prerequisites to Build:

Install dependencies:

sudo apt-get -y install libtool autoconf automake git libelf-dev libssl-dev pkg-config

Clone & Compile

Clone the repository using the following command:

git clone --recursive https://github.com/google/autofdo.git

Note: --recursive fetches perf_data_converter, which contains quipper, and protobuf.

Full build instructions are in the INSTALL file, most can just install the above dependencies, and:

aclocal -I .; autoheader; autoconf; automake --add-missing -c
./configure # or --with-llvm=$(which llvm-config-5.0), for example
make -j 1

Note: do not use the -j to enable parallel build. The configure scripts for the sub-projects fail if run in parallel

Usage

Depending on your compiler, a perf dump can be collected by running one of:

./create_gcov --binary=BINARY --profile=PERF_PROFILE --gcov=OUTPUT
./create_llvm_prof --binary=BINARY --profile=PERF_PROFILE --out=OUTPUT

Inputs

--profile: PERF_PROFILE collected using linux perf (with last branch record). In order to collect this profile, you will need to have an Intel CPU that have last branch record (LBR) support. You also need to have your linux kernel configured with LBR support. To profile:

# perf record -c PERIOD -e EVENT -b -o perf.data -- ./command

Note: EVENT is refering to BR_INST_RETIRED:TAKEN if available. For some architectures, BR_INST_EXEC:TAKEN also works.

--binary: BINARY with debug info. You need to make sure the binary name is the same as the binary you run during profiling. Additionally, you will need to have debug info (i.e. line table) availabe in the binary. This means that you need to compile the binary with "-gmlt" or "-g1". For LLVM, you alse need to have -fdebug-info-for-profiling.

Outputs

For create_gcov: An AutoFDO profile in gcov format. To use the profile with AutoFDO, you need to use the google gcc branch (gcc.gnu.org/svn/gcc/branches/google/gcc-4_8), and pass the following flag to GCC: -fauto-profile=PROFILE_FILE

For create_llvm_prof: An AutoFDO profile in LLVM format. To use the profile with LLVM, you need to use the flag -fprofile-sample-use=PROFILE_FILE. This feature is available in LLVM 3.5 and later.